Completely Stale Transmitter Channel State Information is Still Very Useful

By Mohammad Ali Maddah-Ali, David Tse. IEEE Transactions on Information Theory, 2010

568 citations recorded by the source corpus.

Transmitter channel state information (CSIT) is crucial for the multiplexing gains offered by advanced interference management techniques such as multiuser multiple-input multiple-output (MIMO) and interference alignment. Such CSIT is usually obtained by feedback from the receivers, but the feedback is subject to delays. The usual approach is to use the fed back information to predict the current channel state and then apply a scheme designed assuming perfect CSIT. When the feedback delay is large compared to the channel coherence time, such a prediction approach completely fails to achieve any multiplexing gain. In this paper, we show that even in this case, the completely stale CSI is still very useful. More concretely, we show that in an MIMO broadcast channel with transmit antennas and receivers each with 1 receive antenna, K/1+1/2+···+1/K (>;1) degrees of freedom is achievable even when the fed back channel state is completely independent of the current channel state. Moreover, we establish that if all receivers have independent and identically distributed channels, then this is the optimal number of degrees of freedom achievable. In the optimal scheme, the transmitter uses the fed back CSI to learn the side information that the receivers receive from previous transmissions rather than to predict the current channel state. Our result can be viewed as the first example of feedback providing a degree-of-freedom gain in memoryless channels.

Subfields: Computer Networks and Communications, Electrical and Electronic Engineering

View Paper: https://www.semanticscholar.org/paper/dc6a3f84c64a8f99cc49c44c19229babec93e2b4

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Citations in the corpus

Edge Learning for B5G Networks With Distributed Signal Processing: Semantic Communication, Edge Computing, and Wireless Sensing (2022, unknown): “important focus since the CSI acquisition in MEC is inevitably imperfect owing to channel estimation error [171], limited feedback [172], uncertainty [173], and delays [174].”
Recent Advances in Cloud Radio Access Networks: System Architectures, Key Techniques, and Open Issues (2016, background): “A scheme firstly proposed in [72] considers a transmission scheme that is proved to achieve a larger degree of freedom than one with completely outdated CSIs.”
Topological Interference Management Through Index Coding (2013, background): “From this research, clever interference alignment schemes have emerged that take advantage of channel variations [1], complementary channel states [2], outdated channel states [4], quaternionic structures inherent in complex channels [11], naturally existing channel correlations and coherence patter”
Joint Spatial Division and Multiplexing—The Large-Scale Array Regime (2012, methodology): “Alternatives that do not require CSIT [6] or require only outdated CSIT [7] (without requiring a strict one-slot prediction constraint) have been proposed.”